The present invention relates to a method of manufacturing a semiconductor device. More particularly, it relates to a method of manufacturing a semiconductor device which can introduce a plurality of species of impurities into a desired part without employing a mask.
Heretofore, in case of forming a minute low resistive region by introducing an impurity into a semiconductor by the use of ion implantation, impurity ions have been implanted into a desired region by employing SiO.sub.2 or resist for a mask and irradiating the region with an ion beam about 1 cm in diameter. Needless to say, it is preferable for the higher density of integration of semiconductor elements that an impurity doped region is rendered as small as possible. Besides, in a case where P-type impurity ions and N-type impurity ions need to be implanted using respectively different masks as in case of forming minute periodic P-N junctions in a lateral direction within a semiconductor substrate, the registration accuracy between the masks becomes a problem. For example, the registration accuracy between the masks which is attained when electron beam lithography is employed is limited to approximately 0.15 .mu.m for 3 .sigma..
With a prior art consisting of the lithographic processing of the masks and the ion implantation, accordingly, it has been impossible in view of the registration accuracy between the masks to form the lateral periodic P-N junctions which have pitches of, for example, 0.1 .mu.m or less.
ln this manner, the method of manufacturing a semiconductor device which carries out the conventional ion implantation has hindered enhancement in the integration density of semiconductor elements.
In recent years, however, a technique is being developed wherein, as reported in `Japanese Journal of Applied Physics`, Vol. 22, No. 5, 1983, PL287, ions are implanted into a semiconductor substrate with an impurity ion beam focused to a very small diameter, thereby to form a minute impurity-doped region which has a size nearly equal to the beam diameter. This is based on the fact that liquid metal ion sources from which ions, for example, B.sub.+ and As.sub.30 or Si.sup.+ and Be.sup.+ can be extracted at high brightness have been developed, so it has become possible to readily focus the ions to a diameter of 0.1 .mu.m or less. The circumstances of the developments of such liquid metal ion sources and the applications thereof to semiconductor processes are described in detail in, for example, "Ion Beam/Extensive Applications to Next Generation Process Technology" by Toshio TSURUSHIMA, `Science and Technology in Japan`, July-August, vol. 25, No. 228, 1984, pp. 48-55.
With the focused ion beam, an impurity can be introduced into a minute region within 0.1 .mu.m. However, in case of implanting the ions of another impurity into a region adjacent to the above region, it poses a problem that the positioning accuracy of the ion beams is inferior, so both the species of ions cannot be precisely implanted into the respective predetermined positions. This corresponds to the problem of the registration accuracy between the masks in the case of the conventional ion implantation and forms one serious problem in the practical application of the ion beams.